602 PROF. H. G. SEELET ON THE 



row of the carpus is isolated in the British Museum specimen, but 

 appears to include five small bones in linear series. 



The femur is compressed in opposite directions at the two 

 extremities, but the expansion in either direction is inconsiderable. 



In the specimen K. 536 the tibia measures under 1*6 centimetre and 

 the fibula over 1'8 centimetre long. Hence the bones of the hind limb 

 are very little longer than those of the fore limb. 



The Kimberley specimen of Mesosaurus has shown that in both 

 genera the distal row of the tarsus includes five bones ; but the fifth 

 bone in Mesosaurus is a minute ossification compared with that in 

 Stereosternum. 



The presence of the fifth distal tarsal in Stereosternum induced 

 Prof. George Baur to place the genus in a new order of reptiles 

 under the name ' Proganosauria.' It seems to me probable that in 

 most animals in which there are four distal tarsals the fourth is 

 formed by blending of the fourth and fifth, since the fourth tarsal 

 in them gives attachment to the fourth and fifth metatarsals. And 

 if so, this tarsus is not necessarily so far removed from the mam- 

 malian type as might appear. Nor does the persistence of the fifth 

 distal tarsal necessarily assume the importance assigned to it by Baur. 



Prof. Cope remarks on Stereosternum : — " Its characters are only 

 like those of some of the Urodele Batrachia and the Theromorphous 

 [Anomodont] Beptilia. . . . The vertebrae might be those of a Thero- 

 morph reptile, and the pelvis also agrees with that of those animals. 

 The abdominal rods are found in species of that order referred to the 

 genus Theropleura. The ribs and tarsus are, however, of an entirely 

 different type. The former would refer the genus to the Rhyncho- 

 cephalia or the Sauropterygia, and there is nothing known in its 

 structure which positively forbids either reference, unless it be the 



character of the pelvis The pubis is not so large as the 



ischium, and has a foramen near its posterior border."^ 



The abdominal rods have never been figured in any of the genera 

 in which Prof. Cope has indicated their existence. They are dimly 

 marked on the British Museum Stereosternum, with the same want 

 of definition as the abdominal ribs of Hyperodapedon, They were 

 presumably formed of fibro-cartilage, and not ossified in the same 

 way as in the Kimberley Mesosaurus. The foramen in the pubis is 

 interesting, as it appoximates in position to the notch in the hinder 

 border of the pubis, which characterizes Nothosaurians. 



From the sum of the characters it may be legitimate to include 

 the group within the Anomodontia. But it differs in some remark- 

 able characters which appear to be of sub-ordinal value. The most 

 important of these are the mode of articulation of the dorsal ribs, 

 seen in Mesosaurus ; the Edentate form of the larger limb-bones ; 

 and the structure of the shoulder-girdle. Por this small group 

 thus defined the name 'Mesosauria' would be convenient, because 

 distinctive. 



These African Sauromorpha closely resemble some genera from 

 the Trias of Europe in general form and in characters of the humerus. 

 1 Proe. Am. Phil. Soc. vol. xxiii. (1886) p. 9. 



